The separation of solids from a fluid carrier and the separation of immiscible fluid phases from dispersions and emulsions are typically performed, for example, by various filtration, centrifugation, sedimentation, settling, or electrostatic separation techniques. Previous methods for multiple phase separation, such as solid/fluid phase and fluid/fluid phase separation, have advanced greatly, but there is still a need for even more effective methods to provide a more clarified fluid, while being relatively inexpensive to perform.
Although many conventional processes have been improved, there is yet a substantial need for further improvement. For example, the filtration removal of fines from water often rapidly clogs the filter media to result in greatly reduced flowrates and high pressure drops. Conventional techniques, such as a mechanical scraping, backwash, or media replacement are usually used to minimize this recurring problem. Many of these conventional techniques, however, are cyclic and require the periodic disruption of the filter flow and, hence, necessitate the restoration of the filtration rate after disruption.
This problem has been somewhat alleviated by cross-flow filtration techniques, such as the dynamic rotation of fluid filters and the formation of a turbulent flow in sintered porous tubes. For example, the apparatus of U.S. Pat. No. 3,995,447 to Breton requires the use of rotating disk filters that have hollow disks attached to hollow shafts for removal of the clarified filtrate. This design requires a pressure vessel and a relatively high pressure feed pump to overcome both the centrifugal force developed within the disks and the frictional pressure drop due to the flow in the porous media. The requirement of a pressure vessel adds to the cost of the filter apparatus and the presence of a centrifugal force opposite the direction of the solid particle flow limits the radius and the rotational speed of the disks.
In these axial filtrate collection systems, such as Breton, the centrifugal force limits the disk diameter and rotational speed, and requires that the filter vessel be able to withstand pressures of 50 to 100 psi or more. At these pressures, the colloidal particles in the suspension pass through the porous media close to the shaft of the disks and thereby clog the passageways of the hollow shafts. As a result the filtrate flowing through the central shaft decreases in rate.
The axial removal of filtrate in such a design is inhibited by an increase in the disk diameter or the disk rotational speed. In these devices, the diameter size limits the relation between the rotational speed of the disk and the pressure that can be applied to the disk to overcome the centrifugal force at the peripheral edge of the disk surface. As a consequence, a buildup of particles at the disk surfaces near an axial tube usually occurs, and the layer of particles deposited on this surface increases as the applied pressure is increased.